The major urinary metabolite of the pineal hormone melatonin, 6-hydroxymelatonin is being quantified by gas chromatography-negative chemical ionization mass spectrometry. Urinary excretion rates of this metabolite are being used to determine the possible role of the pineal gland in human reproductive biology-i-.e., its function during pubertal development and throughout the menstrual cycle. A correlative study of plasma melatonin levels, as measured by radioimmunoassay, and 6-hydroxymelatonin in a group of 22 women has been completed. It validates the comparison of plasma levels of the hormone or urinary levels of its metabolite to assess pineal gland production of melatonin in humans. A four year longitudinal collection of urines for melatonin metabolite excretion by young girls through pubertal development has been completed, and the samples are being analyzed. Collaborative studies on the transplantation of neonatal rat pineals into pinealectomized rats have continued, as have collaborative clinical studies on effects of tricyclic antidepressants on the pineal.